Several techniques for determining location based on multiple signals are known. Some, such as the familiar GPS system, employ the differences in transit times among signals from various signal sources, and the receiver. Related techniques encode each of the signals with a common random sequence—synchronized at transmission. The common sequence allows an auto-correlation operation to be performed on the received signal, revealing the time offsets between the different occurrences of this signal sensed by the receiver. The times of transit allow the receiver to be localized relative to the sources.
Another class of techniques relies on differences in strength of signals received from the various signal sources. In a simple implementation, different signals are emitted by different sources. Whichever signal dominates at the receiver indicates the signal source to which the receiver is closest—thereby roughly indicating location. (More sophisticated embodiments consider the strengths of other, less-dominant signals, to yield a more refined location estimate.)
Still another technique relies on count-stamp techniques, as detailed in patent documents U.S. Pat. No. 7,876,266, 20100202300, 20090213828, 20090233621, and 20120309415.
While these methods are most commonly implemented with radio signals, they are similarly useful with audio signals (with corresponding adjustment, where necessary, in view of the slower speed of audio propagation).
In some implementations, the signals from the different sources—from which location is derived—may be steganographically-encoded in other signals. For example, in a retail store, the background music played through speakers in the ceiling may be steganographically encoded with signals that can be used by a shopper's portable device, to determine the shopper's location within the store—by any of the foregoing methods.
(Steganographic encoding is familiar to those versed in digital watermarking. Exemplary technology is detailed in U.S. Pat. No. 6,614,914, and in pending application Ser. No. 13/841,727, filed Mar. 15, 2013, published as 20140108020.)
The ability to determine the location of a user, from audio signals in the environment, enables a great variety of applications.
For example, a user at a movie theatre can be enabled to participate in a role-playing or other game, in which the user's position within the theatre is sensed, and used to determine some aspect of the user's role in the game, or some power or authority that the user is allowed to exercise.
In a home setting, the ability to locate the user allows adaptation of one or more audio signals sent to speakers in a multi-channel audio signal, so that the “sweet spot” of the audio system follows the user at different locations in the listening environment.
The foregoing and other features and advantages of the present technology are detailed below.